#include <stdio.h>

/*
int main(void)
{
 	printf("Hello,World!\n");
 	printf("Welcome to the C language world!\n");
 	printf("Everyone has been waiting for.\n");
	return 0;
}
*/
/*
int main(void)
{
	char c1=97,c2=98;
	printf("%c %c\n",c1,c2);
	printf("%d %d\n",c1,c2);
	return 0;
}
*/
/*
int main(void)
{
	int c1=305,c2=340;
	printf("%c %c\n",c1,c2);
	//305-256=49='0',340-256=89='T';
	printf("%d %d\n",c1,c2);
	return 0;
}
*/
/*
int main(void)
{
	char c1='a',c2='b',c3='c',c4='\101',c5='\116';
 	printf("a%c b%c\tc%c\tabc\n",c1, c2, c3);
 	printf("\t\t\b%c%c\n", c4, c5);	
	 //	\101=1*8^2+1*8^0=65='A';
	 //	\116=1*8^2+1*8^1+6*8^0=64+8+6=78='N';
	return 0;
}
*/
/*
int main(void)
{
	int a,max=0;
	for(int i=0;i<3;i++)
	{
		scanf("%d",&a);
		max=a>max?a:max;
	}
	printf("Max=%d\n",max);
	return 0;
}
*/
/*
int main(void)
{  
	int i,j,m,n;
 	i=8;j=10;
 	//m=++i;           	//i=i+1=9;m=9;
	//n=j++;           	//n=j=10;j=j+1=11;
	m=i++;           	//m=i=8;i=i+1=9;
	n=++j;           	//j=j+1=11;n=j=11;
	printf("%d,%d,%d,%d\n",i,j,m,n);
	return 0;
}
*/
/*
int main(void)
{  
	int i,j;
 	i=8;j=10;
 	//printf("%d,%d\n",i++,j++);         //8 10
 	//printf("%d,%d\n",++i,++j);         //9 11
 	printf("%d,%d,%d,%d\n",i,j,i++,j++); //9 11 8 10
 	return 0;
}
*/
/*
int main(void)
{  
	int i,j,m=0,n=0;
 	i=8;j=10;
 	m+=i++;//m=m+i=m+8=8;i=i+1=9;
	n-=--j;//j=j-1=9;n=n-j=-9;
 	printf("i=%d,j=%d,m=%d,n=%d\n",i,j,m,n);
 	return 0;
}
*/
//int main(void)
//{
//	short i;  
//	i=-2;  
//	printf("\n i:dec=%d,oct=%o,hex=%x,unsigned=%u\n",i,i,i,i);
	//dec=-2;
	/*
		-2: 1000 0000 0000 0000 0000 0000 0000 0010
		i:
		-2:	1000 0000 0000 0010
		   	1111 1111 1111 1101
		   	1111 1111 1111 1110
		%d:	1111 1111 1111 1111 1111 1111 1111 1110	 o377777777776 0xfffffffe
			1000 0000 0000 0000 0000 0000 0000 0001
			1000 0000 0000 0000 0000 0000 0000 0010  -1
		%u:	0000 0000 0000 0000 1111 1111 1111 1110	 4294967294
	*/
//	return 0;
//}
/*
int main(void)
{
	int a,b;
 	float x,y;
 	char c1,c2;
 	//a=3,b=7,85,71.82,aA
 	scanf("a=%d,b=%d",&a,&b);
 	scanf("%f,%e",&x,&y);
	scanf("%c%c%c",&c1,&c1,&c2);             
	printf("a=%d,b=%d,x=%f,y=%f,c1=%c,c2=%c\n",a,b,x,y,c1,c2);	
	//a=3,b=7,x=85.000000,y=71.820000,aA
	return 0;
}
*/
/*
int main(void) 
{  
	float f;
 	f=3.1415;  
	printf("\n %f,%4.3f,%5.3f,%-10.3f,%10.3f\n",f,f,f,f,f);
	//3.141500;
	//3.141;
	//3.141;
	//3.141     ;
	//     3.141;
 	return 0;
}
*/
/*
int main(void)
{
	int a=61,b=62;   
	float c=31.5,d=-68.87;   
	char c1='a',c2='A';
 	printf("\n");
 	printf("a=%d,b=%d\n",a,b);//61 62
 	printf("c=%f,d=%f\n",c,d);//31.500000 -68.870003
 	printf("c=%e,d=%e\n",c,d);//3.150000e+001
 	printf("c1=%c,%c\n",c1,c2);
	return 0;
}
*/
/*
int main(void)
{ 
	int a;   
	float b;   
	char c;
 	scanf("%d,%f,%c",&a,&b,&c);
	printf("a=%d\n",a);
 	printf("b=%f\n",b);
 	printf("c=%c\n",c);
 	return 0;
}
*/
/*
int main(void)
{  
	int a;
 	scanf("%d",&a);
 	printf("a=%d\n", a);
 	char c;
 	c='A';
 	printf("%c",c);
}
*/
/*
int main(void)
{
	int c1,c2;
	c1=getchar();
	c2=getchar();
	putchar(c1);
	putchar(c2);
	printf("\n");
	printf("c1=%c\n",c1);
	printf("c2=%c\n",c2);
	return 0;
}
*/
int main(void)
{
	float pai=3.14f;
	int r,h;
	float c,s,v;
	scanf("%d%d",r,h);
	printf("%d",2*pai*r);
	return 0;
}